Currently, mobile terminals, exemplified by mobile phones, are spreading prolifically, and in order to enable a longer battery operation there has been a demand to make components have even lower power consumption. There are also similar requirements for lower power consumption operations for satellites and space communication equipment. Among these, power consumption of power amplifiers in microwave communication sections is by far the highest overall, and making these power amplifiers highly efficient is the key to achieving a longer operating time for these devices. It is known to make the microwave power amplifiers highly efficient by performing harmonic processing.
Conventionally, class F amplifiers are known as high efficiency microwave power amplifiers. With an class F amplifier a current waveform flowing in an output side of an amplifying transistor is made up of the fundamental+even harmonic components, and a voltage waveform across output terminals of the transistor is made up of the fundamental+odd harmonic components. In this way, it is possible to suppress power loss without overlapping the current waveform and the voltage waveform inside the transistor. Patent publications 1 and 2 below described a class F amplifier circuit used in a distributed constant line that is also suitable for high frequencies. Further, patent publication 2 discloses that it is possible to omit the provision of a partial stub, under fixed conditions.
However, with these techniques, it is basically necessary to provide stubs in accordance with the order of harmonics to be processed. If it is possible to further reduce the number of stubs to be provided, it becomes possible to reduce the size of a circuit and simplify a circuit much more.
On the other hand, in recent years an inverse class F amplifier has been proposed for carrying out harmonic processing that is different from the above described class F amplifiers. With an inverse class F amplifier a current waveform flowing in an output side of an amplifying transistor is made up of the fundamental+odd harmonic components, and a voltage waveform across output terminals of the transistor is made up of the fundamental+even harmonic components. In this way, it is possible to suppress power loss without overlapping the current waveform and the voltage waveform inside the transistor (refer to non-patent publication 1 below). Also, with an inverse class F amplifier, verification experiments have been performed, using an external tuner, adjusted up to the third harmonic (refer to non-patent publication 2 below). Although dependent on operating conditions, by using an inverse class F amplifier it is considered to enable higher efficiency power amplification than class F (refer to non-patent publication 3 below).
In order to obtain a voltage waveform for the above-described inverse class F operation, the load impedance at the output terminals of the amplifying transistor should be made zero for odd harmonics. Similarly, in order to obtain a current waveform, the load impedance for the even harmonics should be made infinite.
In order to realize this type of inverse class F amplifier, as shown in patent publication 3 below, for example, there is a method of connecting two reactance circuit networks that have pole and zero points set for each harmonic based on a first or second Foster method to output terminals of an amplifying transistor series and in parallel. In doing this a load impedance that alternates repeatedly between infinity and zero is realized for an increase in harmonics.
However, accompanying the move towards high frequency wireless communication of recent years, in the case of an amplifier operating at 6 GHz, for example, the frequency of the seventh harmonic becomes 42 GHz. Amplification transistors that operate in this frequency band do exist, but if the frequency of about 42 GHz is reached the self-resonant of the reactance elements becomes too great. Therefore, when the operating frequency is high, it is difficult to realize an inverse class F operation with the method of patent publication 3 below.
On the other hand, with respect to a class F amplifier, there has also been proposed a circuit for obtaining desired impedance conditions by using a distributed constant line that can also be applied to high frequencies (refer to patent publications 1 and 2 below). However, this method is specific to the class F operation, and it is not possible to obtain an inverse class F amplifier circuit even by adjusting this circuit.
Accordingly, for an inverse class F amplifier, if it is possible to provide a high frequency processing circuit that uses a distributed constant line, it will be possible to provide an inverse class F amplifier that is also capable of operating at high frequency.
Patent publication 1: Japanese unexamined patent publication No. 2001-111362
Patent Publication 2: Japanese unexamined patent publication No. 2003-234626
Patent Publication 3: Japanese unexamined patent publication No. 2005-117200
Non-patent publication 1: A. Inoue, et al., “Analysis of class-F and inverse class-F amplifiers,” IEEE MTT-S Int. Microwave Symp. Dig., Boston, Mass. June 2000, pp. 775-778.
Non-patent publication 2: C. J. Wei, et al., “Analysis and experimental waveform study on inverse class-F mode of microwave power FETs,” IEEE MTT-S Int. Microwave Symp. Dig., Boston, Mass. June 2000, pp. 525-528.
Non-patent publication 3: Y. Y. Woo, et al., “Analysis and experiments for high-efficiency class-F and inverse class-F power amplifiers,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 5, pp. 1969-1974, May 2006.
The present invention has been conceived in view of the above-described situation.
A first object of the present invention is to provide a high frequency processing circuit capable of miniaturizing a circuit, and an amplifier circuit using this high frequency processing circuit.
A second object of the present invention is, with respect to a class F or inverse class F amplifier that are known as a high efficiency power amplifier, to provide a high frequency processing circuit capable in principle of processing infinite order harmonics, and an amplifier circuit using this high frequency processing circuit.
A third object of the present invention is to provide a harmonic processing circuit for an inverse class F amplifier, capable of operating in a high frequency region such as the microwave band and the millimeter waveband, and an amplifier circuit using this harmonic processing circuit.
A fourth object of the present invention is to provide a harmonic processing circuit for an inverse class F amplifier, capable of adjusting load impedance with respect to a fundamental, without changing impedance conditions with respect to all harmonics, and an amplifier circuit using this harmonic processing circuit.